As a conventional quantum dot infrared photodetector is known an infrared photodetector which comprises a layer structure of an intermediate layer and a quantum dot layer including a plurality of quantum dots whose band gap is narrower than that of the intermediate layer alternately stacked and detects photocurrent generated by the excitation of electrons or holes in the quantum dots when infrared radiation is applied to the layer structure to thereby detect infrared radiation.
In this infrared photodetector, the intermediate layer of GaAs or others with quantum dots of InAs or others buried in is a photoabsorbing unit layer, and this photoabsorbing unit layer is stacked plural times to thereby from the layer structure (see Japanese Laid-open Patent Publication No. 10-256588).